As is well known, fiber optic technology is a rapidly growing field with vastly expanding commercial applicability. As with all technologies, fiber optic technology is faced with certain practical difficulties. In particular, the design and fabrication of arrays of optical elements that enable the efficient switching and coupling between input optical elements and output optical elements in an optical network is a significant consideration of designers, manufacturers, and users of optical systems. Optical systems commonly use laser generated light beams, to carry information through optical fibers and are directed through complex optical paths with the assistance of optical switching elements, routers and other like components. Other applications include wavelength routers that demultiplex incoming signals into individual wavelength and then switch in the nonblocking fashion single wavelengths between outputs, laser beam deflectors in laser printers, bar code reading devices and others.
FIG. 1 schematically illustrates a portion of a fiber optic network 100. In the depicted embodiment, network 100 routes optical signals through fiber optic lines L from node to node to form an interlaced ring-mesh network structure. Many other configurations of network structures are possible. In the depicted embodiment, the fiber optic lines L are interconnected at optical nodes 101, 102, 103, 104, 105, and 106. The optical signals are directed to their desired destination by optical switching. Typically, this switching is accomplished at the optical nodes 101, 102, 103, 104, 105, and 106 (also referred to herein as switching nodes). Each switching node 101, 102, 103, 104, 105, and 106 accommodates a plurality of fiber optic lines L which comprise input fibers and output fibers. It is the selecting of and switching between these input fibers and output fibers that define the optical paths which route optical signals to their desired target destinations.
FIG. 2(a) is a simplified schematic illustration showing an overview of bi-directional optical cross-connect switching array system 200. The system 200 includes fiber arrays 202 and 204 for passing light beams into and out of the switching array system 200. Each fiber array 202, 204 comprises a plurality of fiber optic transmission lines (a portion of which are shown here by fibers 210, 211, 220, and 221). For convenience, fiber array 202 shall be referred to as an incoming fiber array 202 and the fiber array 204 shall be referred to as an outgoing fiber array 204. However, it should be remembered that due to the bi-directional nature of the switching array system 200, the terms incoming and outgoing are relative.
Light beams carry information throughout the optical network. The light beams are directed to their final destination by passing through switching array systems 200 which direct the light beams to the desired destination. Electronic control circuitry 230 is used to dynamically control the switch 200 configuration. The control circuitry 230 can include, among other elements, position sensitive detectors, demultiplexing circuitry, photodetectors, position sensing detectors, amplifiers, decoding circuitry, servo electronics, digital signal processors, communication hardware, and an application programming interface. The control circuitry directs entering light beams to the desired exit fibers.
The following simplified illustration describes how a light beam can be switched from one of the incoming fibers in array 202 to a selected one of the fibers in array 204. Such description is also applicable to switching a light beam between any selected fiber in array 204 to a selected fiber in array 202.
In the depicted illustration, the light beam 231 exits the fiber 210 (and in preferred embodiments, passes through a lens array (not shown) so that the beam propagates without significant divergence) onto the reflector array 218. Servo electronics of the control circuitry 230 initiate deflection in a reflector 218′ of the reflector array 218 to direct the light beam 231 along an optical path 232 to a desired fiber 220 (in fiber array 204) using a signal from position detection array 234. By changing the deflection of the reflectors (e.g., 218′) of the reflector array the light beams can be switched to enter any selected outgoing fiber 204. Also, the deflection of each of the reflectors 218′ can be altered in very small ways to fine tune light beam optical characteristics. The reflector 218′ deflection can be adjusted in response to instructions contained within the data streams of the light beam 231. Alternatively, reflector 218′ deflection can be adjusted in response to instructions provided externally via an application programming interface of, for example, the control circuitry. Other methods of adjusting reflector 218′ deflection known to those having ordinary skill in the art can also be used.
A light beam can be switched from one outgoing fiber to another outgoing fiber, by changing reflector deflection angle. For example, if light beam 231, 232 is to be switched from fiber 220 into another outgoing fiber 221, the controller circuitry 230 sends appropriate instructions to the servo electronics which reposition the reflector 218′ so that beam 231 is redirected along optical path 233 to fiber 221. Typically, the beams (e.g., 232, 233) pass through a lens array (not shown) which focuses and couples the light beam (here 233) into the outgoing fiber (here 221). It should be noted that although fibers have heretofore been referred to as belonging to the incoming fiber arrays 202 or the outgoing fiber arrays 204, such fiber arrays are bi-directional. In such bi-directional embodiments, light beams also travel from the outgoing fibers in the outgoing fiber array 204 to incoming fibers in the incoming fiber array 202. This is done in the same way as light beams traveling from incoming fibers in the incoming fiber array 202 to outgoing fibers in the outgoing fiber array 204. Also shown in FIG. 2(a) are the position-sensitive-detectors 234, which feed the position-error-signals to the controller circuitry 230.
The switching array system 200 is shown as one-dimensional in the embodiment of FIG. 2(a) for clarity. In preferred embodiments the aforementioned arrays are two-dimensional. For example, in an embodiment with a two-dimensional reflector array 218, there are rows and columns, or some other two-dimensional arrangement of reflectors. The other arrays and alignment structures are similarly two-dimensional in some embodiments. In addition, the overall system is shown as two-dimensional in FIG. 2(a). In preferred embodiments, the system is three-dimensional, as the additional dimension in and out of the plane of the paper can be advantageously used to position the various components and minimize the dimensions of the hardware.
It should be noted that although FIG. 2(a) depicts the switching device 200 as having a single reflector array 218, many embodiments include two or more reflector arrays instead of just one with or without additional plane reflectors. One such embodiment is schematically illustrated in FIG. 2(b). FIG. 2(b) is a simplified schematic illustration showing an overview of two-reflector array bi-directional optical cross-connect switching array system 201. The system 201 includes fiber arrays 202 and 204 for passing light beams into and out of the switching array system 201. The fiber arrays 202, 204 include a plurality of fiber optic transmission lines (a portion of which are shown here by fibers 210, 211, 220, and 221). Here, the incoming light beam 234 is directed toward a first reflector array 217 which reflects the beam 234, 235 onto a second reflector array 219 and then into the desired outgoing fiber (here, 221). Switching may be accomplished by altering the deflection of the reflectors of the first reflector array 217 or by altering the deflection of the reflectors of the second reflector array 219 or by altering the deflection of the reflectors of the first reflector array 217 and the reflectors of the second reflector array 219 at the same time. In this example, the path of light beam 234 is altered by the deflection of first reflector 217′ which directs the light beam 234 onto the altered beam path 236 onto second reflector 219′ and into outgoing fiber 220. Additionally the control circuitry (not shown) controls the reflectors of both the first reflector array 217 and the second reflector array 219. Although structurally somewhat different from the previously discussed embodiment 200, the principles of operation of such multiple reflector array switches 201 are similar. Similar switching functions can be performed using alternative switching configurations. For example, one embodiment can use combined first and second sets of movable reflectors and one fixed reflector. An optical beam can be switched by reflection of an input beam from a movable reflector onto a fixed reflector and from this reflector back onto a movable reflector and into output fiber. Number of reflectors in the combined array is the same as total number of reflectors in two physically separate arrays. Many other configurations are used and known by those having ordinary skill in the art.
MEMS switching arrays can also be used in wavelength routers. One embodiment of such a wavelength router is depicted in FIG. 3. Using wavelength division multiplexing light beams of several wavelengths can be optically transmitted using the same fiber. For example, a single fiber can carry light beams comprising k signals at k wavelengths. These light beams of many wavelengths are coupled from a fiber 331 into a wavelength division demultiplexer 334. The demultiplexer 334 can be based on arrayed waveguide gratings, interference filters, or fiber Bragg gratings. The illustration of FIG. 3 uses an arrayed waveguide grating 334 as a wavelength division demultiplexer. Multi wavelength light beam 345 enters into the first free space region 335, is separated into individual wavelengths in grating 333 and exits through the second free space region 336 where light beams at k wavelengths are spatially separated. Light at each specific wavelength is coupled into linear fiber array that directs light beams onto a lens array 342. Relatively collimated light beams such as 343 and 344 propagate toward mirrors of the first array 337. The light at each specific wavelength is reflected from one mirror in the first array 337 onto a specific mirror of the second mirror array 338 from which the light is directed onto focusing lenses 339 and into a selected output fiber 351. The mirror arrays 337 and 338 can be one-dimensional arrays in order to match the spatial distribution of the light beams or two-dimensional arrays. Mirror arrays 337 and 338 are formed by bi-axial (bi-axially actuated) mirrors.